Iron temperature method of controlling blast furnaces



June 27, 1967 K H. GEE ETAL IRON TEMPERATURE METHOD OF CONTROLLING BLAST FURNACES Original Filed July 51, 1962 Temperature x |OOF Start of Cost 3 Maximum (2750F) 37 mlnuies duration of cast 3 Sheets-Sheet l 4 End of Casi Finish Casi INVENTORS Kenneth H. Gee Merle H.Schmidi 11.1. LLLLL K. H. GEE ETAL 3,328,162

3 Sheets-Sheet 2 June 27, 1967 IRON TEMPERATURE METHOD OF CONTROLLING BLAST FURNACES Original Filed July 31, 1962 3 2 228cm: 8 7 6 5 1 389' 8mm 2 2 2 2 -Et -1A eowwmw mii mu 0mm. 09m

x 0 m mn. m me 009 om m m 0095 2 us: 335 uomuv mu OWE 00$ 2m OOm Omfi mo 00E 09m hr. 009 om v 7.09 x E EuQEE.

INVENTORS Kenneth H. Gee Merle H. Schmidt June 27, 1967 H. GEE ETAL 3,328,162

mow TEMPERATURE METHOD OF CONTROLLING BLAST FURNACES Original Filed July 31, 1962 3 Sheets-Sheet 3 Fig,

Temperature x 100 F 22 u 2 2nd Cost u 3rd 1 22 Time I 8 I 3 5 3 cu '3 F u 0 9 O7 3' 2s a 2a 5 2? 5 27 o I O 26 26 1 cu l I 25 f 25 3 1 24 T 24 E i i INVENTORS Kenneth H. Gee Merle H. Schmidt United States Patent 3,328,162 IRON TEMPERATURE METHOD OF CON- TRGLLING BLAST FURNACES Kenneth H. Gee, Bethlehem, and Merle H. Schmidt,

Johnstown, Pa, assignors to Bethlehem, Steel Corporation, a corporation of Delaware Continuation of application Ser. No. 213,820, July 31, 1962. This application June 21, 1965, Ser. No. 476,366 14 Claims. (CI. 7541) This is a continuation of application Ser. No. 213,820, filed July 31, 1962, and now abandoned.

The general object of the present invention is to provide an improved method of controlling the operation of a metallurgical blast furnace.

Control of temperature within the blast furnace is of major importance to good operation. When the furnace temperature is maintained within the proper range and other operating variables are in control, the result is smooth furnace operation, good tonnage and quality iron. If furnace temperatures become too high, the tendency is for the furnace to go on pressure and encounter uneven movement of burden, lose some tonnage, and make high silicon iron. When furnace temperature falls too low, the furnace tends to make high sulfur iron. The corrective changes made when the furnace is too hot include reduction of hot blast temperature, increase in the ore load, reduction of coke, increase in moisture addition to the hot blast, or such other changes as may be the operators practice. The reverse corrective changes are made for a cold furnace.

Until now no practical means of closely controlling furnace temperature has been developed. The operator has relied mainly upon the visual appearance of the tuyeres, flush slag, and iron. The iron silicon content (i.e., the silicon content of the iron being tapped) is first estimated during the cast. Confirmation by laboratory analyses entails a one to two hour delay. In addition to the delay, laboratory analysis of iron silicon does not lead to reliable furnace temperature control because iron silicon is affected by factors other than temperatures. For example, an increase in iron silicon is generally considered an indication that the furnace temperature is rising, but a decrease in slag basicity will also cause an increase in iron silicon. This may be wrongly interpreted as a hot furnace condition even though the furnace temperature is in the proper range. Also, as will be shown, iron silicon often will not reflect a cooling-off condition when the iron first starts losing temperature, thereby delaying corrective changes.

The primary object of the present invention is to provide a simple and practical method for controlling the thermal balance of a balst furnace in order to promote its consistent operation.

In carrying out our invention we make a continuous measurement of the temperature of the stream of molten iron leaving the furnace during a cast. The temperatures of the iron, as continuously deter-mined during the cast, are utilized as a basis for adjustment of the thermal balance of the furnace to maintain the furnace temperature within proper range. This contributes to smoother furnace operation and results in improved quality iron and increased tonnage.

The objects and advantages of this invention will be more clearly understood from the following description, with reference to the accompanying drawings in which:

FIG. 1 shows an iron tempearture curve which was typical for the particular blast furnace from which it was obtained under the operating conditions then existing. This curve shows normal values for the furnace, i.e., it was neither heating up nor cooling down.

FIG. 2 shows a series of iron temperature curves taken at a time when the furnace operators were still using iron silicon as a basis for making corrections in operating conditions.

FIG. 3 shows a series of three casts showing the application of the invention in the operation of a furnace which was undergoing a cooling condition.

FIG. 4 shows a series of iron temperature curves showing the application of the invention to the operation of a furnace experiencing a higher than normal heating condition.

FIG. 5 shows a single iron temperature curve showing the application of the invention in the operation of a furnace that was becoming hotter than normal.

For measuring the temperature of the iron during the cast, we prefer to use an immersion thermocouple located in the stream of molten iron beyond the skimmer and before the dam, and to make a chart of the temperatures throughout the cast. In a copending application Ser. No. 118,454, filed June 20, 1961, there is described an improved device for continuously determining the temperature of blast furnace iron during casting. This device is an immersion thermocouple which is extremely accurate, even at the elevated temperatures of molten iron. The output of this thermocouple can be recorded automatically in known ways. FIGS. 1 through 5 are illustrative of temperature curves obtained in this manner. However, this invention is not limited to the use of the specific thermocouple described in said application.

For any particular furnace there are periods when, for a given set of operating conditions, the furnace is said to be operating smoothly or in balance. Throughout these periods a minimum of adjustment of the thermal balance is required for operation, and production is high. Iron temperatures measured continuously during the casts throughout this period of smooth operation, when the furnace is neither heating up nor cooling down, willresult in curves of similar appearance. When running smoothly the furnace from which the curve of FIG. 1 was obtained produced similar curves for other casts at that time. On this curve point 1 represents the start temperature which occurs with in a few minutes after the tap hole is opened and just after normal flow of iron has been established. Point 2 denotes the start of the slag flow from the furnace. Point 3 signifies the maximum temperature attained during the cast. Point 4 is the temperature at the end of the cast.

In carrying out this invention, measurements of iron temperatures during a cast are utilized by the furnace operator as a guide for making changes in the thermal balance of the furnace, in one or more of the follwing ways:

(a) The operator compares the temperatures at points 1, 2 and 3 of the iron temperature curve of the cast currently being made with the temperatures at points 1, 2 and 3 of the iron temperature curves of the preceding cast or casts and adjusts the thermal balance of the furnace in accordance as the temperatures at said points of the curve of the cast currently being made differ from the temperatures at said points of the curve of the preceding cast or casts; or

(b) The operator compares the temperatures at points 1, 2 and 3 of the iron temperature curve of the cast currently being made with the temperatures at points 1, 2 and 3 of the normal iron temperature curve and adjusts the thermal balance of the furnace in accordance as the temperatures at said points of the curve of the cast currently being made differ from the temperatures at said points of the normal curve; or

(c) The operator compares the change from the start of the curve to appearance of slag of the iron temperature curve of the cast currently being made with the change from the start of the curve to appearance of slag of the iron temperature curve of the preceding cast or casts and adjusts the thermal balance of the furnace in accordance as said change from the start of the curve to appearance of slag of the iron temperature curve of the cast currently being made differs from the change from the start of the curve to appearance of slag of the iron temperature curve of the preceding cast or casts; or

(d) The operator compares the change from the start of the curve to appearance of slag of the iron temperature curve of the cast currently being made with the change from the start of the curve to appearance of slag of the normal iron temperature curve and adjusts the thermal balance of the furnace in accordance as said change from the start of the curve to appearance of slag of the iron temperature curve of the cast currently being made differs from said change from the start of the curve to appearance of slag of the normal iron temperature curve; or

(e) The operator compares the change from the appearance of slag to the end of the curve of the iron temperature curve of the cast currently being made with the change from the appearance of slag to the end of the curve of the iron temperature curve of the preceding cast or casts and adjusts the thermal balance of the furnace in accordance as said change from the appearance of slag to the end of the curve of the cast currently being made differs from the change from appearance of slag to the end of the curve of the iron temperature curve of the preceding cast or casts; or

(f) The operator compares the change from the appearance of slag to the end of the curve of the iron temperature curve of the cast currently being made with the change from appearance of slag to the end of the curve of the iron temperature curve of the normal curve and adjusts the thermal balance of the furnace in accordance as said change from the appearance of slag to the end of the curve differs from said change from the appearance of slag to the end of the curve of the normal iron temperature curve. For a given furnace and for a given set of operating conditions and practice there is a normal or average increase in temperature from point 2 to point 3. Between points 1 and 2, for the same furnace and furnace practice, there is generally a small increase in temperature, one not nearly as pronounced as the gradient between points 2 and 3. A temperature increase between these points greater than normal indicates that the furnace is heating up, while a temperature increase less than normal indicates that the furnace is cooling. A decrease in iron temperature in place of the normal increase between points 1 and 2 represents a cooling furnace. A decrease in iron temperature between points 2 and 4 without an intervening increase represents a fast cooling furnace which requires strong corrective action.

Under present methods of control, as mentioned above, the operator relies upon his experience using the visual appearance of several factors and upon iron silicon analysis to control his furnace temperature. Under the circumstances he is making a guess, based upon his previous ex-- perience, that the changes he makes will bring or keep the furnace in balance. Some changes the operator makes may take as long as eight to ten hours to reveal their effect at the hearth level; any errors in judgment on his part may tend to move the furnace out of balance.

By contrast, the use of the iron temperature curve for a particular blast furnace, for a given set of operating conditions, as described in this application, can be utilized to control the operation of that furnace and to make prompt corrections for any deviation from normal temperature conditions.

FIG. 2 shows a series of iron temperature curves from a blast furnace. At the time these curves were made the furnace operators were still utilizing visual appearance of several factors and iron silicon analysis to control the furnace. The curves were observed by the operators, but did not enter into their actual control of the furnace. At the start of this series the burden per charge for this furnace was 36,000 pounds of ore, 9,000 pounds of stone,

16,000 pounds of coke, 2,600 pounds of open hearth slag and 4,000 pounds of scrap. Other furnace operating factors were 90,000 c.f.m. wind, 6 grains moisture, 2,000 c.f.m. of natural gas and a hot blast temperature of 1500 F. The curves show the furnace (1) in a normal temperature condition (1st cast), (2) giving early warning of the furnace cooling down (2nd cast), (3) in a cold condition (3rd, and 4th casts), (4) recovering from cold condition (5th cast), and (5) in a higher-than-normal temperature condition (6th cast). Within each curve is the silicon and sulfur analysis of the iron for that particular cast.

The temperature curve for the first cast is a typical curve, at that time, for this blast furnace when it was in its normal temperature condition and was neither heating up nor cooling down. The iron silicon of 0.96% is also average for this furnace during that period. The hot blast temperature changes made after the first cast were based upon tuyere observations, iron analysis, and the appearance of slag and iron.

The temperature curve for the second cast shows a decrease in the temperature throughout the cast. Under the iron temperature system of control this signifies a strong cooling-off of the furnace and would serve as a warning to the operator. In this case, the operator relied upon the usual visual factors during the cast, confirmed by the laboratory iron silicon analysis (1.00%), which indicated no furnace cooling. In most cases when blast furnaces cool down suddenly, the iron silicon values do not decrease immediately. It is during this initial cooling down period that the iron temperature method of controlling a blast furnace is most valuable.

The temperature curve for the third cast shows the furnace to be considerably colder, and the poor quality of the iron (0.47% silicon and 0.105% sulfur) reflects the cold furnace condition. The furnace operator promptly added eight extra buckets of coke at the beginning of the cast when he saw the poor appearance of the iron which appeared to be low in silicon and high in sulfur. Iron temperatures confirmed the interpretation of these visual factors. The lack of increase in iron temperature during the cast, especially the latter part of the cast, shows the furnace to be still cooling down. After this cast and after the appearance of the following flush slag which looked poor, the operator reduced the ore load to aid in heating the furnace.

The temperature curve for the fourth cast reflects a continued cooling for some time after the end of the third cast. That this cooling-off was arrested before the start of the fourth cast is shown by the normal temperature increase (60 F.) after appearance of slag. The iron continues to be low in silicon (0.41%) and high in sulfur (0.081%).

The temperature curve for the fifth cast has a start temperature similar to the previous cast, showing that heating up of the furnace did not begin until sometime after the end of the fourth cast. The large increase in temperature after appearance of slag (190 F.) shows the effects of the eight extra buckets of coke added at the start of the third cast. The improved iron analysis (0.68% silicon and 0.049% sulfur) indicated that the furnace was recovering, but the full extent of recovery is better shown by the iron temperature curve, particularly by the large increase in temperature after slag.

The temperature curve for the sixth cast shows a normal start temperature. The increase F.) in temperature, above normal for this period, after appearance of slag shows the furnace to be still heating up and becoming hotter than normal, probably showing the effect of removal of 1000 pounds of ore per charge just before the fourth cast. The iron analysis shows higher-thanaverage silicon (1.35%) and below average sulfur (0.020%) in accordance with a hot furnace condition.

FIG. 3 shows a series of three casts made in accordance with this invention and illustrating a cooling furnace. At the start of this series the burden charge for the furnace was 35,800 pounds of ore, 9,200 pounds of stone, 17,100 pounds of coke, 2,600 pounds of open hearth slag and 3,200 pounds of scrap. Other furnace operating factors were 87,000 c.f.m., 6 grains of moisture, 2,700 c.f.m. of natural gas and a hot blast temperature of 1500 F. In the first cast of the series both the maxi-mum iron temperature (2760 F.) and the silicon (1.12%) were slightly higher than normal. The temperature values for the second cast indicated a cooling furnace because the temperature increase (25 F.) after the appearance of slag was lower than normal for that period. Accordingly, the operator adjusted the thermal balance by increasing the hot blast temperature by 50 F. immediately after the cast in order to keep the furnace from cooling down. Had silicon analysis and visual inspection of the iron been the only guides available for making corrective changes, no change would have been made on the basis of the 1.13% silicon as compared to the 1.12% silicon of the previous cast, Consequently cast three would have been colder with higher sulfur. As a result of the prompt increase in hot blast temperature, the cast showed normal iron temperature and good analysis (1.04% Si and 0.023% S). Succeeding casts were in line with the normal curves for that period.

FIGURES 2 and 3 present two examples of a cooling furnace. In both series of casts there occurred belownormal increases in iron temperature after the appearance of slag. By the practice of this invention, the cooling condition shown in the second cast of FIG. 3 was corrected by the prompt increase of 50 F. in hot blast temperature at the end of the cast. The cooling condition shown in the second cast of FIG. 2, however, was more severe than in the second cast of FIG. 3, as indicated by the decrease in iron temperature after slag appearance and warranted a stronger corrective change. However, because at the time, the operator was relying on visual means of control, even though he observed the iron temperature curve, this corrective action was delayed until the cooling condition had become more severe.

When iron temperature measurments indicate that a furnace is heating up beyond desired limits the corrective actions that can be'taken to adjust the thermal balance are just the opposite of those made on a cooling furnace. These actions may include 1) a decrease in hot blast temperature, (2) a decrease in coke burden, (3) an increase in moisture content of the hot blast, (4) an increase in ore burden, or (5) a suitable combination of the first four.

FIG. 4 shows a series of three casts made in accordance with this invention where iron temperature aided the operator in promptly correcting a heating condition in the furnace. In the first cast of the series the starting temperature was in accord with the initial temperatures of the casts of the same period. However, the iron temperature rose more rapidly than normal, and halfway through the cast it reached the level of the maximum temperature of the preceding cast. This upward trend continued, and the iron temperature reached a peak of about 2730 F, approximately higher than that of the earlier cast. The furnace operator interpreted this upward trend and higher maximum temperature as signaling a hotter furnace and acted accordingly. Immediated after the cast he adjusted the thermal balance of the furnace by adding a grain of moisture, and two hours later reduced his coke charge.

The temperature curve for the second cast shows that the operator was correct in his interpretation of the trend of the curve of the first cast. Almost the entire second cast curve lies above the maximum temperature (2730 F.) of that of the first cast, and the maximum temperature of 2800" F. is considerably hotter than normal for this furnace, at that time. The increase in iron silicon to 1.21% as compared to 1.05% of the first cast confirmed the iron temperatures signal that the furnace was heating 6 up. Shortly after the cast the operator added another grain of moisture to lower the furnace temperature.

The third cast shows the results of the corrective action taken by the operator. The maximum temperature of 2785 F. is somewhat lower than that of the preceding cast, and, significantly, most of the curve of this cast indicates temperatures appreciably lower than those of the second cast. The furnace was slowly returning to its normal temperature range, and the iron silicon was in line with what was expected. The iron temperature curve for the subsequent cast, not shown, indicated that the furnace was still slowly cooling and the curve was very similar to the uual curve for that period.

FIG. 5 show the iron temperature curve of a single cast wherein the configuration of the curve, even before the end of the cast, led the furnace operator to take corrective action. The two casts immediately preceding this cast were similar in appearance to other curves for casts on the same furnace during the period. The temperature at the start of this curve was slightly below normal, but the greater than usual slope of the curve to a temperature of 2725 F. at appearance of slag was interpreted by the operator as indicating that the furnace was heating up. Consequently, shortly after the appearance of slag, but before the maximum temperature, the operator adjusted the thermal balance of the furnace by adding one grain of moisture to correct for the heating action of the furnace. The peak temperature of 2760 F., after the cooling correction was made, confirmed the operators interpretation of the early part of the curve.

It will be understood that is not necessary, at all times, to make a comparison between the curve of the cast currently being made and that of the normal curve and/or the curve of the preceding cast. A marked change in increase or decrease in temperature over those portions of the curve between points 1 and 2 or between points 2 and 3 is informative as to the degree of change taking place in the thermal state of the furnace. Accordingly, the operator can make changes in the thermal balance of the furnace during the cast, as these evidences present themselves.

The method of operating a blast furnace by the use of iron temperature curves taken continuously during a cast may be utilized in conjunction with other means of furnace control. The prior means of control are not eliminated, they may still be utilized. Iron silicon analyses, estimated and actual, are still made. When a furnace is heating up the iron temperatures will rise and the iron silicon content will also increase, one aflirming the other. However, when a furnace is cooling the iron silicon content will not generally drop until some time, usually one cast later, after the iron temperatures have signaled a cooling furnace.

It must be emphasized that iron temperature curves differ for each furnace and for the same furnace after changes in operating practice. The initial slope of the curve and the normal temperature increase after appearance of slag may change from furnace to furnace and for different furnace practices; it is determined from experience during a period when the furnace is operating smoothly.

Although certain novel features of our invention have been shown and described, it will be understood that changes and modifications can be made in the procedure without departing from the spirit of the invention or the scope of the appended claims.

We claim: a

1. The method of controlling the operation of a blast furnace which comprises:

(a) determining, by means including temperature measuring means, the iron temperature curve for a first cast of iron from said furnace,

(b) determining, by means including temperature measuring means, the iron temperature curve for the next succeeding cast of iron from said furnace,

(c) adjusting the thermal balance of said furnace to cause said furnace to heat up when said determination for said next succeeding cast shows that said furnace is cooling down and to cause said furnace to cool down when said determination for said next succeeding cast shows that said furnace is heating up.

2. The method of controlling the operation of a blast furnace which comprises:

(a) determining, by means including temperature measuring means, a normal temperature curve for iron cast from said furnace under a given set of operating conditions,

(b) determining, by means including temperature measuring means, a temperature curve for a subsequent cast of iron from said furnace under said operating conditions,

(c) adjusting the thermal balance of said furnace to cause said furnace to heat up when said determination for said subsequent cast shows that said furnace is cooling down and to cause said furnace to cool down when said determination for said subsequent cast shows that said furnace is heating up.

3. The method of controlling the operation of a blast furnace which comprises:

(a) determining, by means including temperature measuring means, for a first cast of iron from said furnace the iron temperatures at (1) start of cast, (2) appearance of slag, and (3) maximum temperature;

(b) determining, by means including temperature measuring means, for the next succeeding cast of iron from said furnace the iron temperatures at (1) start of cast, (2) appearance of slag, and (3) maximum temperature;

(c) determining the changes between the temperatures determined in step (a),

(d) determining the changes between the temperatures determined in step (b),

(e) adjusting the thermal balance of said furnace to cause said furnace to heat up when said determinations of temperatures made in steps (a) and (b) show that said furnace is cooler and that the temperature changes determined in step (d) are smaller than the temperature changes determined in step (c), and to cause said furnace to cool down when said determinations of temperatures made in steps (a) and (b) show that said furnace is hotter and that the temperature changes determined in step (d) are larger than the temperature changes determin d in step (c).

4. The method of controlling the operation of a blast furnace which comprises:

(a) determining, by means including temperature measuring means, for a given set of operating conditions for iron cast from said furnace the normal iron temperatures at (1) start of cast, (2) appearance of slag, and (3) maximum temperature;

(b) determining, by means including temperature measuring means, for said operating conditions for iron subsequently cast from said furnace the iron temperatures at (1) start of cast, (2) appearance of slag, and (3) maximum temperatures;

(c) determining the changes between the temperatures determined in step (a),

(d) determining the changes between the temperatures determined in step (b),

(e) adjusting the thermal balance of said furnace to cause said furnace to heat up when said determinations of temperatures made in steps (a) and (b) show that said furnace is cooler and that the temperature changes determined in step (d) are smaller than the temperature changes determined in step (c), and to cause said furnace to cool down when said determinations of temperatures made in steps (a) and (b) show that said furnace is hotter and that the temperature changes determined in step (d) are larger than the temperature changes determined in step (c).

5. The method of controlling the operation of a blast furnace which comprises:

(a) determining, by means including temperature measuring means, a normal temperature curve for iron cast from said furnace under a given set of operating conditions from the start of the cast to the appearance of slag,

(b) determining, by means including temperature measuring means, a temperature curve for a subsequent cast of iron from said furnace under said operating conditions from the start of the cast to the appearance of slag,

(c) determining the change in said normal curve from the start of the cast to the appearance of slag,

(d) determining the change in the curve of said subsequent cast from the start of the curve to the appearance of the slag,

(e) adjusting the thermal balance of said furnace to cause said furnace to heat up when said temperature curves determined in steps (a) and (b) show that said furnace is cooler and that the change determined in step (d) is smaller than the change determined in step (c) and to cause said furnace to cool down when said temperature curves determined in steps (a) and (b) show that said furnace is hotter and that the change determined in step (d) is larger than the change determined in step (c).

6. The method of controlling the operation of a blast furnace which comprises:

(a) determining, by means including temperature measuring means, the iron temperature curve for a first cast of iron from said furnace from the start of the cast to the appearance of slag,

(b) determining, by means including temperature measuring means, the iron temperature curve for the next succeeding cast of iron from said furnace from the start of the cast to the appearance of slag,

(c) determining the change in the curve of said first cast from the start of cast to the appearace of slag, (d) determining the change in the curve of said next succeeding cast from the start of cast to the appearance of slag,

(e) adjusting the thermal balance of said furnace to cause said furnace to heat up when said temperature curves determined in steps (a) and (b) show that said furnace is cooler and that the change determined in step (d) is smaller than the change determined in step (c) and to cause said furnace to cool down when said temperature curves determined in steps (a) and (b) show that said furnace is hotter and that the change determined in step (d) is larger than the change determined in step (c).

7. The method of controlling the operation of a blast furnace which comprises:

(a) determining, by means including temperature measuring means, a normal temperature curve for iron cast from said furnace under a given set of operating conditions from the appearance of slag to the maximum temperature,

(b) determining, by means including temperature measuring means, a temperature curve for a subsequent cast of iron from said furnace under a given set of operating conditions from the appearance of slag to the maximum temperature,

(c) determining the change in said normal temperature curve from the appearance of slag to the maximum temperature,

(d) determining the change in the curve of said sub- 9 sequent cast from the appearance of slag to the maximum temperature,

(e) adjusting the thermal balance of said furnace to cause said furnace to heat up when said temperature curves determined in steps (a) and (b) show that said furnace is cooler and that the change determined in step (d) is smaller than the change determined in step (c) and to caused said furnace to cool down when said temperature curved determined in steps (a) and (b) show that said furnace is hotter and that the change determined in step (d) is larger than the change determined in step (c).

8. The method of controlling the operation of a blast furnace which comprises:

(a) determining, by means including temperature measuring means, the iron temperature curve for a first cast of iron from said furnace from the appearance of slag to the maximum temperature,

(b) determining, by means including temperature measuring means, the iron temperature curve for the next succeeding cast of iron from said furnace from the appearance of slag to the maximum temperature,

(c) determining the change in the curve of said first cast from the appearance of slag to the maximum temperature,

((1) determining the change in the curve of said next succeeding cast from the appearance of slag to the maximum temperature,

(e) adjusting the thermal balance of said furnace to cause said furnace to heat up when said temperature curves determined in steps a) and (b) show that said furnace is cooler and that the change determined in step (d) is smaller than the change determined in step (c) and to cause said furnace to cool down when said temperature curves determined in steps (a) and (b) show that said furnace is hotter and that the change determined in step (d) is larger than the change determined in step (c).

9. The method of controlling the operation of a blast furnace which comprises:

(a) determining, by means including temperature measuring means, for a first cast of iron from said furnace the iron temperatures at (1) appearance of slag, (2) maximum temperature, and (3) end of cast;

(b) determining, by means including temperature measuring means, for the next succeeding cast of iron from said furnace the iron temperatures at (1) appearance of slag, (2) maximum temperature, and (3) end of cast;

(c) determining changes between the temperatures determined in step (a),

(d) determining the changes between the temperatures determined in step (b),

(e) adjusting the thermal balance of said furnace to cause said furnace to heat up when said determinations of temperatures made in steps (a) and (b) show that said furnace is cooler and that the temperature changes determined in step (d) are smaller than the temperature changes determined in step (c), and to cause said furnace to cool down when said determinations of temperatures made in steps (a) and (b) show that said furnace is hotter and that the temperature changes determined in step (d) are larger than the temperature changes determined in step (c).

10. The method of controlling the operation of a blast furnace which comprises:

(a) determining, by means including temperature measuring means, for a given set of operating conditions for iron cast from said furnace the normal iron tem peratures at (0) determining the changes between the temperatures determined in step (a),

(d) determining the changes between the temperatures determined in step (b),

(e) adjusting the thermal balance of said furnace to cause said furnace to heat up when said determinations of temperatures made in steps (a) and (b) show that said furnace is cooler and that the temperature changes determined in step (d) are smaller than the temperature changes determined in step (c), and to cause said furnace to cool down when said determinations of temperatures made in steps (a) and (b) show that said furnace is hotter and that the temperature changes determined in step (d) are larger than the temperature changes determined in step (c).

11. A method of controlling the operation of a blast furnace which comprises:

furnace which comprises:

(a) continuously, by means including temperature measuring means, measuring the temperature of iron being cast from said furnace, and

(b) adjusting the thermal balance of said furnace to cause said furnace to heat up when the highest temperature of the iron is that temperature at the start of the cast, and the temperature at the end of the cast is below the temperature at the start of the cast.

13. The method of controlling the operation of a blast furnace which comprises:

(a) determining, by means including temperature measuring means, for a given set of operating conditions for iron cast from said furnace the normal iron temperatures at (1) start of cast, and (2) appearance of slag;

(b) determining, by means including temperature measuring means, for said operating conditions for iron subsequently cast from said furnace the iron temperatures at (1) start of cast, and (2) appearance of slag;

(c) determining the change between the temperatures determined in step (a),

(d) determining the change between the temperatures determined in step (b),

(e) adjusting the thermal balance of said furnace to cause said furnace to heat up when said determinations of temperatures and temperature changes show that said starting temperatures are the same and that the temperature change determined in step (d) is smaller than the temperature change determined in step (c) and to cause said furnace to cool down when said determinations of temperatures and temperature changes show that said starting temperatures are the same and that the temperature change determined in 1 1 step (d) is greater than the temperature change determined in step (c).

14. The method of controlling the operation of a blast furnace which comprises:

(at) determining for a given set of operating conditions for iron cast from said furnace the normal iron temperatures at 1) appearance of slag, and (2) maximum temperature;

(b) determining for said operating conditions for iron subsequently cast from said furnace the iron temperature at (1) appearance of slag, and (2) maximum temperature;

(0) determining the change between the temperatures determined in step (a),

(d) determining the change between the temperatures determined in step (b),

(e) adjusting the thermal balance of said furnace to cause said furnace to heat up when said determinations of temperatures and temperature changes show that said starting temperatures are the same and that References Cited 15 York, 1942, page 300.

Holtby, F., Transactions of the American Society for Metals, December 1941, pages 863-880.

DAVID L. RECK, Primary Examiner.

20 H. W. TARRING, Assistant Examiner. 

1. THE METHOD OF CONTROLLING THE OPERATION OF A BLAST FURNACE WHICH COMPRISES: (A) DETERMINING, BY MEANS INCLUDING TEMPERATURE MEASURING MEANS, THE IRON TEMPERATURE CURVE FOR A FIRST CAST OF IRON FROM SAID FURNACE, (B) DETERMINING, BY MEANS INCLUDING TEMPERATURE MEASURING MEANS, THE IRON TMEPERATURE CURVE FOR THE NEXT SUCCEEDING CAST OF IRON FROM SAID FURNACE, (C) ADJUSTING THE THERMAL BALANCE OF SAID FURNACE TO CAUSE SAID FURNACE TO HEAT UP WHEN SAID DETERMINATION FOR SAID NEXT SUCCEEDING CAST SHOWS THAT SAID FURNACE IS COOLING DOWN AND TO CAUSE SAID FURNACE TO COOL DOWN WHEN SAID DETERMINATION FOR SAID NEXT SUCCEEDING CAST SHOWS THAT SAID FURNACE IS HEATING UP. 